It is known to provide hinge devices which rotatably couple a first member to a second member and to provide the hinge device with a degree of friction to provide positional, or angular control of a first member as it is rotated relative to the second member. Common applications for such friction hinges are in laptop and notebook-type computers to allow a user to position a liquid crystal display (LCD) screen at a selected location. While such frictional hinge devices have been acceptable for selectively positioning an LCD screen at a position where the display screen is merely used to read the matter displayed on the screen, such conventional frictional hinges are problematic when used in conjunction with touch-screen technology.
For portable, laptop or notebook computers which incorporate either pen-based functions or for point-of-sale terminals which include more basic touch-screen technology, the conventional friction hinges do not provide sufficient torque to hold the display screen in a selected location, considering the weight of the display as well as the torque generated from a user pressing a pen or finger on the display screen, given the allowable space for the hinge in the product. Even if a portable computer were designed to provide sufficient space to receive a conventional friction hinge which is large enough to provide torque capable of keeping the display screen in a selected location, such a device would exhibit the undesirable characteristic of producing a high level of torque at all times. That is, by producing a high level of torque at all times, the user must then exert a larger force on the display screen to rotate it from one position to another, making it difficult to position, and clumsy, from an ergonomic perspective.
Furthermore, if a user would attempt to close a display screen to the base of a portable computer which has a frictional hinge which produces high frictional torque at all times, the significant residual stress which remains in the casing or housing from the excessive torque would prevent the two halves of the housing from meeting uniformly together. As such, it would be necessary to greatly increase the wall thickness in the housing halves to account for the higher stresses encountered. Such a design variation is directly contrary to producing a portable computer which should be as lightweight as possible.
With respect to touch-screen technology, it has been known to (1) place a wedge-shaped block under the touch panel to keep it at a certain fixed angle; (2) firmly mount the touch panel at a fixed angle to a base; (3) include a ratchet-type mechanism; or (4) have some other complicated mechanism which requires the user to adjust a couple of elements simultaneously to achieve the proper height and angle of the touch panel. Concerning the wedge-shaped block and firmly mounting approaches, they do not permit positioning (rotation) of the touch panel. With respect to a ratchet mechanism, there is a risk for breakage of the ratchet teeth if the user applies a large external torque to the display screen.
Thus, a need has arisen for a lockable hinge assembly which will enable a user to selectively provide a high amount of frictional torque having a first state of operation wherein the frictional hinge assembly is unengaged and provides substantially zero frictional torque to allow the display screen to be freely movable with respect to the base of the portable computer, and a second position wherein a high amount of frictional torque is provided to lock the display screen with respect to the base of the portable computer to permit the use of touch-screen technology.
The present invention provides a lockable hinge assembly for selectively rotatably locking a first hinge member to a second hinge member which is relatively small, lightweight and simple to manufacture, so that it may easily be incorporated in a device whose main object is to be portable. The lockable hinge assembly of the present invention is lockable with only a relatively small actuation force in a relatively short actuation stroke. The lockable hinge assembly of the present invention achieves simultaneous application of torque-holding capability in two directions (i.e., clockwise and counterclockwise), while only requiring a single actuating stroke. Further, if a user exceeds the frictional torque capacity of the lockable hinge assembly of the present invention, the hinge assembly merely acts as an overrunning clutch.